JP2005311952A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus capable of reading an accurate image by acquiring reflection data excepting an optical dot gain from a document such as a printed material. <P>SOLUTION: As an occupancy ratio of an image forming region, an image area rate is determined for each pixel based on transmission image data resulting from receiving light transmitted through a document by an image area rate calculation section 5. A reflection image data calculation section 6 determines corrected reflection image data which are corrected for each pixel, based on reflection image data resulting from receiving reflection light from the document in the case of irradiating the document at a predetermined angle and the image area rate. An optical dot gain which is incurred when reading an image formed from a reflection image from a document such as a printed material, is excluded and reflection image data according to area gradations can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus that reads information on a document from an image of reflected light by irradiating light on a paper surface such as a document with illumination means.

  As an image forming method used in a copying machine, there are an electrophotographic method and an inkjet method, and as a printing method in a printing machine, letterpress printing, screen printing and the like can be mentioned. Formed or printed on paper (herein, paper and plastic film including a gelatin layer in which a powder of white pigment such as titanium oxide is dispersed and a polymer layer such as polyethylene are provided) For an image, a phenomenon called mechanical dot gain occurs due to the image forming process. Mechanical dot gain is a phenomenon in which the dot size formed on paper with toner or ink is larger than the dot size to be reproduced. Further, when an image formed on paper is viewed, a phenomenon called optical dot gain occurs in which color material density is distributed around the dots due to optical conditions and blurring occurs.

  FIG. 17 is a diagram for explaining the phenomenon of optical dot gain when one dot formed on paper is observed with a light-receiving CCD (Charge Coupled Device). As shown in FIG. 17A, in addition to a region where each pixel has a single color material region, a plurality of color material densities are distributed around the dots, resulting in an optical dot gain. It can be seen that the pixel exists. Further, the value of the reflection density at that time is entered in FIG. The values in the intermediate data area indicated by 10 and 140 are not accurate reflection data because an optical dot gain is generated.

  FIG. 18 is a schematic diagram showing the state of the optical path around the dots. As shown in FIG. 18, the optical dot gain is obtained when the light incident on the color material layer is reflected in the lower layer paper and returned through the color material layer in the area where the printed matter is observed. It does not occur in the optical path 21 and the optical path 22 when the light incident on the paper is reflected and returned as it is in the underlying paper. On the other hand, the light incident on the color material layer is reflected in the lower layer paper and returned without passing through the color material layer, and the light incident on the paper is reflected in the lower layer paper. As for the optical path 24 in the case of returning through the color material layer, either incident light or reflected light passes through the color material layer, so that the amount of light at that time is a dot around the color material layer. An optical dot gain is observed as a blur.

  When an image reading device reads an image of a printed matter having a color material layer formed on paper, it is desired to obtain image data in a state excluding the optical dot gain. In an image reading apparatus, a method is generally employed in which light is irradiated from a direction of 45 degrees with respect to a document surface and light reflected in a 0 degree direction (based on a direction perpendicular to the document surface) is received. . However, in this case, the read image data is data including an optical dot gain as described above, and cannot be said to be accurate image data excluding optical behavior due to scattering in paper. .

  As a solution to such an optical dot gain phenomenon, Japanese Patent Laid-Open No. 8-116407 adopts spot illumination that irradiates with a spot having a size equal to or smaller than the size of the minimum pixel area that can be detected by a line sensor. The optical dot gain is removed. In the technique disclosed in this publication, the optical dot gain can be removed when the light receiving area is entirely the color material area or the paper area, but when the light receiving area is the boundary between the color material area and the paper area. The optical dot gain cannot be completely removed.

In Japanese Patent Laid-Open No. 2003-344032, an image obtained by removing optical dot gain as much as possible is obtained by using a combination of a gas laser and an expander as a reflection light source and making the incident light source parallel light. The method disclosed in this publication inevitably causes scattering in paper, so that the optical paths 23 and 24 shown in FIG. 2 remain, and an optical dot gain is generated.
JP-A-8-116407 (paragraphs [0029] to [0030], FIGS. 1 to 3) JP 2003-344032 A (paragraphs [0025] to [0029], FIGS. 1 and 2)

  As described above, in the conventional image reading apparatus, it is very difficult to read an accurate image obtained by removing the optical dot gain from a document such as a printed matter.

  Therefore, it does not depend on only the reflected image data obtained by receiving the reflected light from the original when the original is irradiated at a predetermined angle, but is obtained by receiving the transmitted light transmitted through the original. There is a problem to be solved in that the reflection data from which the optical dot gain is removed is obtained by using the image area ratio obtained as the occupation ratio of the image forming area based on the transmission image data.

  An object of the present invention is to provide an image reading apparatus capable of reading an accurate image by acquiring reflection data obtained by removing an optical dot gain from a document such as a printed matter.

  In order to solve the above problems, an image reading apparatus according to the present invention calculates an image area ratio as an occupancy ratio of an image forming area for each pixel based on transmitted image data obtained by receiving transmitted light transmitted through an original. And the image area ratio calculated by the reflected image data obtained by receiving the reflected light from the original when the original is irradiated at a predetermined angle and the image area ratio calculated by the image area ratio calculator. A reflection image data calculation unit for obtaining corrected reflection image data corrected for each pixel based on the rate is provided.

  According to this image reading apparatus, it is possible to obtain reflection image data in accordance with the area gradation, except for the optical dot gain that has been generated when reading the printed image by the reflection image so far. Thereby, accurate reflected image data excluding optical behavior generated in the color material boundary region due to light scattering on paper can be acquired. Further, since the transmitted light is received by the light receiver without being substantially scattered, an accurate print area ratio can be obtained.

  In this image reading apparatus, the image area ratio calculation unit can obtain the image area ratio using a predetermined function with the transmittance of each pixel constituting the transmission image data as a variable. With this configuration, conversion from transparent image data to print area ratio data can be performed by function calculation. Further, it is not necessary to have an LUT or the like in which an influence change due to the paper type of the printed material is recorded, and it can be used for general purposes. In this case, the predetermined function may be a linear function that converts the image area ratio of both pixels indicating the maximum transmittance and the minimum transmittance among the transmittances to correspond to 100% and 0%, respectively. it can. Since the function is a linear function with the transmittance as a variable, the calculation is simple and the configuration of the image area ratio calculation unit can be simplified.

  In this image reading apparatus, both pixels indicating the maximum transmittance and the minimum transmittance exist in the transmission image data. However, the reflection image data calculation unit calculates the minimum transmittance and the maximum transmittance in the transmission image data. The reflectance as the reflected image data of each of the pixels indicating the above is defined as a maximum density-corresponding reflectance and a minimum density-corresponding reflectance, and for each pixel, the maximum density-corresponding reflectance and the minimum density The corrected reflected image data is obtained by weighting and adding the image area ratio of the pixel and its complementary image area ratio (a value obtained by subtracting the image area ratio from 1) to the corresponding reflectance. Can be calculated. That is, for each pixel, the image area obtained from the transmission image data includes the maximum density correspondence reflectance which is the reflectance of the portion where the image exists and the minimum density correspondence reflectance which is the reflectance of the portion where the image does not exist. The corrected reflection image data is calculated by taking a weighted average of the rate and the complementary image area rate.

  As a configuration of the image reading apparatus, light from one light source can be selectively guided to the transmission irradiation unit or the reflection irradiation unit. The light from the light source is guided to the transmission irradiation unit through the first waveguide to obtain transmission image data from the document, or is guided to the reflection irradiation unit through the second waveguide to obtain reflection image data from the document. . The image reading apparatus also includes a control unit, which sets the output of the light source depending on whether the irradiating unit for transmission or the irradiating unit for reflection is operated, and either the first waveguide or the second waveguide. Select. By configuring the image reading apparatus in this way, one light source output device can be used without providing each of the reflection and transmission output light source devices, and the processing problem of the amount of heat generated by the two light source output devices and the output light amount. The image reading apparatus can be used at a low cost, including the problem of the time until the image becomes stable.

  In this image reading apparatus, it is preferable that the control unit performs control so as to read image data within a predetermined range as transmission image data or reflection image data. By controlling in this way, one data acquisition range is determined by the number of pixels of the light receiver (CCD), and the amount of one movement of the optical system unit in the main scanning direction and the sub scanning direction is for each light receiving range. As the number of pixels of the light receiver (CCD) increases, the number of readings decreases, so that the reading speed improves.

  In this image reading apparatus, it is preferable that the control unit integrally controls the transmission irradiation unit and the reflection irradiation unit. By integrally driving the transmission irradiation unit and the reflection irradiation unit, it is possible to perform measurement without causing a positional shift in the light reception range of the transmission image data and the reflection image data by the optical system. Moreover, it is not necessary to mount each drive circuit and mechanism, and the drive part of both trading company parts can be implement | achieved by one drive system.

  Furthermore, in this image reading apparatus, it is preferable that the control unit is controlled to read the reflected image data first and then read the transmitted image data. By determining the reading order in this way, the output light amount of the light source is increased from the reflection image acquisition with a low light output to the transmission image acquisition with a high light output, so the time until the output light becomes stable is reversed. Less than the case.

  The present invention is configured as described above, and the image area ratio as an occupation ratio of the image forming area based on the transmission image data obtained by the image area ratio calculation unit receiving the transmitted light transmitted through the document. For each pixel, and the reflected image data calculation unit receives the reflected light from the original when the original is irradiated at a predetermined angle, and calculates the image area ratio. Since the corrected reflected image data corrected for each pixel is obtained based on the image area ratio obtained by the printing unit, an optical dot gain that has conventionally occurred when reading an image from a reflected image from a document such as a printed matter. The reflection image data according to the area gradation can be obtained. Thereby, accurate reflected image data excluding optical behavior generated in the color material boundary region due to light scattering on paper can be acquired. Further, since the transmitted light is received by the light receiver without being substantially scattered, an accurate print area ratio can be obtained.

  Embodiments of the present invention will be specifically described below based on the drawings. FIG. 1 is a schematic view showing a lower part and an upper part of an image reading apparatus according to the present invention. In FIG. 1, reference numeral 31 indicates a light source for reflection and a light receiving CCD unit, reference numeral 32 indicates a light source for transmission, reference numerals 33a and 33b indicate positioning members in the main scanning direction, and reference numerals 34a and 34b indicate positioning members in the sub-scanning direction. ing. A glass plate (original platen) is installed on the upper surface of the lower part of the image reading apparatus (not shown). The light source for reflection and light receiving CCD unit 31 is provided at the lower part of the image reading apparatus, and the light source for transmission 32 is provided at the upper part of the image reading apparatus. The transmissive light source 32 has a larger light quantity than the reflective light source.

  FIG. 2 is a side view of the image reading apparatus, and shows that the lower part and the upper part of the image reading apparatus of FIG. 1 are connected. The positioning members 33a and 33b in the main scanning direction and the positioning members 34a and 34b in the sub-scanning direction are strictly positioned by their concave and convex shapes (not shown). In FIG. 2, reference numerals 41 to 46 denote the following components. That is, 41 is an operation belt for driving the optical system unit 30 in the main scanning direction, 46 is an operation belt for driving the optical system unit 30 in the sub-scanning direction, 42 is a reflective white film, and 43 is a reflective white film. A rotating roller for driving the film 42, a support wire 44 for supporting the reflective white film 42, and a support roller 45 for supporting the reflective white film 42 and being driven when the reflecting white film rotating roller 43 is driven. is there. The upper part of the image reading apparatus is operated by the positioning members 33a and 33b in the main scanning direction and the positioning members 34a and 34b in the sub scanning direction extending simultaneously in the vertical direction (perpendicular to the main scanning direction and the sub scanning direction). A document such as a printed material can be set between the lower part and the upper part of the image reading apparatus. The optical system unit 30 has a corner on which a document is placed (for example, a left shoulder angle) as a home position, and is operated by the operation belt 41 in the main scanning direction and by the operation belt 46 in the sub-scanning direction. Until it reaches the home position (for example, the lower right corner). The home position is detected by a signal from a positioning sensor (not shown), and the optical system unit 30 is controlled by this signal.

  FIG. 3 is a view of the upper structure of the image reading apparatus shown in FIG. 2 as viewed from above and below. The upper structure of the image reading apparatus includes a reflective white film 42, a rotating roller 43, support wires 44 and 44, and a support. The configuration of the roller 45 is included. The front side of the reflective white film 42 is a white surface 42a painted with barium sulfate or the like, and the back side of the reflective white film 42 is a black surface 42b. The reflective white film 42 hardly transmits light as a whole. Although not shown, the transmissive light source 32 is disposed at an intermediate position between the rotating roller 43 and the support roller 45. The reflective white film 42 is larger than the originals of all sizes that can be read by the image reading apparatus and has a size larger than the glass plate installed at the lower part of the image reading apparatus. The support wires 44, 44 are installed on both sides of the reflective white film 42, and are connected to the rotating roller 43 through the support roller 45. The rotating roller 43 has a motor therein, and the supporting wires 44 and 44 are driven by rotating the rotating roller 43 by the output of the motor, so that the reflective white film 42 can be operated. Note that there are two upper and lower rotating rollers 43, each having a different driving rotation direction. In FIG. 2, the upper part is counterclockwise and the lower part is clockwise. With the above configuration, when the upper rotating roller 43 is driven and the support wire 44 is wound, the lower rotating roller 43 is driven, and the reflective white film 42 can be moved to a position directly above the transmissive light source 32. When the lower rotating roller 43 is driven to wind the support wire 44, the upper rotating roller 43 is driven, and the reflective white film 42 can be moved to just below the transmissive light source 32.

  The amount of light output from the light source 32 for transmission needs to be sufficient to transmit the original, but since the amount of light is different from that of the light source 31a for reflection, it is necessary to prepare a separate light source output device. However, such a configuration not only incurs high costs due to the need for two light source output devices as image reading devices, but also causes a problem with the amount of heat generated from the two light source output devices and the amount of light from the light source during startup. Problems such as waiting time until stabilization will occur. Therefore, in this image reading apparatus, a light source output device that outputs a minimum amount of light is prepared as the transmission light source 32, and a method of dividing the output light from the light source output device with a fiber is adopted (the entire image reading device). (See FIG. 7 for a block diagram of FIG. 7). The fiber adopts a glass fiber diameter of 500 μm so that it can withstand the heat of the high output light source, and the transmission light source fiber (first waveguide) and the reflection light source fiber (second waveguide) are provided at two locations of the light source output device. To the output units (transmission light source output unit and reflection light source output unit). Switching between which output unit outputs light is performed according to a signal from the control unit. Each light amount output is set by the user in advance, and here, the output is 200 W as the transmission light source 32 and 100 W as the reflection light source. Each of the transmission light source output section and the reflection light source output section is provided with a glass-made feedback fiber having a fiber diameter of 100 μm so as to feed back the output light quantity to the light source output device. The output is controlled so that the amount of feedback light is kept constant in the light source output device.

  FIG. 4 is a cross-sectional view of the image reading apparatus in the sub-scanning direction at the time of reflection image measurement. The light source (CCD) 31b and the transmissive light source 32 in the reflection light source and light receiving CCD unit 31 are arranged in a direction perpendicular to the original, and the reflection light source and light reception CCD unit 31 and the transmission light source 32 are optical. The system unit 30 moves one unit at a time in the main scanning direction (backward direction in the drawing), and after reading is completed, moves one unit in the sub-scanning direction and repeats reading in the main scanning direction. The one unit is the width of the light receiving range of the light receiver 31b in the main scanning direction and the sub scanning direction, respectively (see FIG. 16). As a result, as the number of pixels of the light receiver 31b increases, the number of readings is reduced, so that the reading speed is improved.

  The reflection light source 31a and the light receiver 31b in the reflection light source and light receiving CCD unit 31 maintain a general 45/0 relationship (incident angle is 45 °, light reception angle is 0 °) for reflection image measurement. . At the time of reflection image measurement, control is performed so that the white film for reflection 42 is positioned on the back side of the document. The reflective white film 42 is intended to obtain a sufficient contrast of the original. At this time, the transmissive light source 32 is not turned on, but only the reflective light source 31a is turned on, and the reflected light reflected from the original is received by the light receiver 31b.

  FIG. 5 is a cross-sectional view of the image reading apparatus in the sub-scanning direction during transmission image measurement. The positional relationship of each member is substantially the same as the positional relationship shown in FIG. 4. However, in order to obtain a transmission image of the original, the white film for reflection 42 is rotated above the light source 32 for transmission, Control is performed so that the reflective white film 42 is not positioned between the light source for reflection and the light receiving CCD unit 31. The mechanical operation method of the light source for reflection and the light receiving system unit 31 is the same as that at the time of reflection image measurement. However, the light source for reflection 31a is not turned on, only the light source for transmission 32 is turned on, Light is received at 31b.

  Since the measurement position accuracy of the reflected image and the transmitted image is very important for reading the image, the optical system unit 30 is returned to the home position after all the reflected image data of the document is acquired, and the rotating roller 43 is driven to perform reflection. Control is performed so that the white film 42 is positioned above the light source 32 for transmission. At this time, if the white film for reflection 42 is operated as it is, the document position may be shifted. Therefore, the positioning members 33a and 33b in the main scanning direction and the positioning members 34a and 34b in the sub scanning direction are moved in the vertical direction (in FIG. 4). It is operated in an environment where the white film for reflection 42 and the original are separated from each other. The operations of the positioning members 33a and 33b in the main scanning direction and the positioning members 34a and 34b in the sub-scanning direction are performed up and down about 5 mm from the initial position where the document is set by an internal motor (not shown). Thus, control is performed so that the original position is not shifted by the movement of the reflective white film 42.

  By the operations of the light receiving unit and the reflective white film 42, it is possible to eliminate the positional deviation of the light receiving range of the transmission image data and the reflection image data. Further, since the transmission light source 32, the reflection light source, and the light receiving CCD unit 31 operate as an optical system unit 30 by being integrated by an operation belt, separate driving system circuits are provided for the transmission light source 32, the reflection light source, and the light receiving CCD unit 31. The light receiving CCD unit 31 can be realized only by the drive circuit and mechanism for reflection and light receiving CCD units without providing a mechanism.

  FIG. 6 is a flowchart of a reading method by the image reading apparatus, and FIG. 7 is a control block diagram. The image reading apparatus 1 includes a reflection image reading unit 2 that reads a reflection image of a document, a transmission image reading unit 3 that reads a transmission image of a document, a light source output device 4 that supplies a light amount necessary for reading an image, A print area ratio calculation unit 5 that calculates a print area ratio from transmission image data of a transmission image read by the transmission image reading unit 3, a reflection image data calculation unit 6 that calculates reflection image data, and acquired image data are stored. A memory 7, an image output device 9 that outputs image data calculated by the reflected image data calculation unit 6, an interface 10 that exchanges signals with the host computer 11 when an image is output to the host computer 11; Reflection image reading unit 2, transmission image reading unit 3, light source output device 4, printing area ratio calculation unit 5, reflection image data calculation unit 6, memory 7 and interface A control unit 8 for controlling the Esu 10 consists of host computer 11 for capturing data after the control and image processing to the control unit 8.

  The image output device 9 may be a display device such as a CRT (Cathode Ray Tube) or a liquid crystal panel, or a variety of media such as paper, OHP paper, etc., by an electrophotographic method, a thermal transfer method, an ink jet method, or the like. It may be a printing apparatus that records on a recording medium and forms an image. The control unit 8 predetermines the processes of the reflected image reading unit 2, the transmitted image reading unit 3, the light source output device 4, the print area rate calculation unit 5, the reflected image data calculation unit 6, and the memory 7 in the control unit 8. This is a device (CPU: Central Processing Unit) that sends control signals to each of the above processing units according to certain processing and distributes control according to instructions from the host computer 11 and sends control signals to various devices. . The interface 10 receives a signal from the control unit 8 and is read by the image reading device 1 when an instruction from the host computer 11 is sent to the control unit 8 or an instruction to output an image to the host computer 11 is given. (For example, USB (Universal Serial Bus), SCSI (Small Computer System Interface), IEEE (Institute of Electrical and Electronic 4)).

  Reading processing by the image reading apparatus 1 is performed as follows. First, the document is set between the lower part and the upper part of the image reading apparatus 1. The original is set so that the position of the original falls within a predetermined reading size. Examples of the setting position include matching the left shoulder portion of the document with the left shoulder of the lower glass plate of the image reading apparatus 1. Next, when the controller 8 receives an image reading start signal from the host computer 11, the light source output device 4 is warmed up, and after the output light quantity enters a stable period, image reading is started. Whether or not the light quantity stabilization period has been entered is determined by the fact that the sensor receives light output from the feedback fiber installed at the output section of the light source output device 4, and the difference in the amount of change in light quantity per unit time is substantially constant. It is judged by checking. Next, an original image is acquired. In the present embodiment, the reflection image data is acquired first, and then the transmission image data is acquired. This is because, when considering the stability of the light output of the light source output device 4, the output of light after the increase is more stable when the output is increased when the output is increased and when the output is decreased. is there. On the contrary, if the transmission image data is acquired first, it takes a considerable time until the reflection light source output is stabilized.

  Reflected image data from the original is converted into a digital signal by an A / D (analog / digital) converter (not shown), and various kinds of data generated in the optical system (illumination system, imaging system, imaging system). The shading correction for removing the distortion is performed, and the reflectance of each pixel is sequentially stored in the first memory 7 a prepared in advance in the memory 7. The output of the reflection light source 31a at this time uses a reflection light source output set in advance by the light source output device 4. Next, the optical system unit 30 is moved one unit at a time in the main scanning direction and then repeated, and then the unit is moved one unit at a time in the sub-scanning direction and the process is repeated, thereby completing the reflection image acquisition for all the documents.

  When the reflection image acquisition of all the originals is completed, a signal indicating the completion of reflection image acquisition is sent to the control unit 8, and the light receiving system unit 30 is set to the home position according to the signal from the control unit 8 so that the next transmission image acquisition can be performed. Moved to. Then, the reflective white film 42 is moved from the position between the light source 32 and the light source 32 for transmission to the position above the light source 32 for transmission, and the light output of the light source output device 4 is switched from reflective to transparent.

  Thereafter, transmission image data of the same pixel is acquired from the same home position as when the reflection image data was acquired, the transmission light source 32 is turned on, and the transmittance received by the light receiver 31b is prepared in the memory 7 in advance. Are sequentially stored in the second memory 7b. The subsequent operation is the same as that at the time of reflection image data acquisition. When the transmission image data is read, the transmittance is calculated based on the amount of light received in the absence of the document, so that the optical system is not corrected as in the case of reading the reflection image data. The light quantity of the reference light source may be read every time reading in each sub-scanning direction is completed at an end portion where no document is placed, or may be read at a predetermined frequency. As the reference value, an average value may be obtained for the entire image, or may be set for each image data read at a predetermined frequency.

Next, the printing area ratio calculation unit 5 calculates the printing area ratio in each pixel from the transmittance of each pixel. As a method for calculating the print area ratio, the pixel data having the highest transmittance is Tmax and the pixel data having the lowest transmittance is Tmin among the transmittance data of all the documents stored in the second memory 7b. Then, the print area ratio S of each pixel is obtained using the equation (1), and is stored in the third memory 7 c in the memory 7. That is, the print area ratio S of each pixel is the area ratio data normalized with a minimum of 0% and a maximum of 100%.
S (i, j) = [{Tmax−T (i, j)} / {Tmax−Tmin}] × 100
... (1)
S (i, j): Print area ratio of pixel position i in the main scanning direction and pixel position j in the sub scanning direction T (i, j): Transmission of pixel position i in the main scanning direction and pixel position j in the sub scanning direction rate

  As another printing area ratio calculation method, the relationship between the transmittance and the printing area ratio of several types of paper is stored as data in a LUT (Lookup Table: Lookup Table) in advance, and the user designates the paper type of the document, for example. Thus, a paper type is selected from the LUT, the relationship between the transmittance and the print area ratio is referred to, and the transmittance of each pixel in the second memory 7b is converted into the print area ratio. The relationship between the transmissivity and the print area ratio is stored as data in the LUT, and there is no color material in each pixel, that is, from the transmissivity data of only the paper or the pixel with the highest transmissivity, the paper in the LUT There is a method of selecting a seed, referring to the relationship between the transmittance and the print area ratio, and converting the transmittance of each pixel in the second memory 7b into a print area ratio.

  8 to 10 show the results of investigating the relationship between the printing area ratio and the transmittance in samples in which an image is formed with toner color material on various papers in order to confirm the effectiveness of the expression (1). 8 shows data for coated paper, FIG. 9 shows data for 64 g paper, and FIG. 10 shows data for 128 g paper. The plot on the graph is actual measurement data, and the area ratio is calculated from the ratio of the number of pixels with a high density value and the number of low density pixels with the image analysis software binarized with a threshold value of 50%. . On the other hand, the straight line is the result of calculating the transmittance with an area ratio of 100% as Tmax, measuring the transmittance with an area ratio of 0% as Tmin, and calculating with the formula (1). The actual measurement values are arranged almost on the straight line of the equation (1), and it is understood that the equation (1) has sufficient accuracy when taking measurement errors into consideration. This indicates that the transmitted light is received by the light receiving CCD without being substantially scattered in the paper. 9 and 10 show similar results, and it can be seen that equation (1) is universally effective even when the paper changes. The LUT stores a plurality of actually measured values (print area ratio values corresponding to the transmittance) as shown in FIGS. 8 to 10 for each paper type.

  Next, the print area ratio of the pixel having the highest print area ratio is extracted from the print area ratio data of each pixel stored in the third memory 7c, and the address (ia, ja) of the pixel is recorded. If there are a plurality of pixel addresses (ia, ja) at this time, the first extracted pixel address (ia, ja) is used. The reflectance data corresponding to the address (ia, ja) of this pixel is read out from the reflectance data of each pixel stored in the first memory 7a, and Ri (maximum density-corresponding reflectance; numerical value as reflectance) Save itself as a minimum). If there is a pixel with a print area ratio of 100%, the address (ia, ja) of that pixel is recorded, the subsequent detection operation is stopped on the spot, and the address (ia, ja) of that pixel is recorded. The reflectance data corresponding to may be read and stored as Ri.

  Similarly, the area ratio data of the pixel with the lowest printing area ratio is searched from the printing area ratio data of each pixel stored in the third memory 7c, and the address (ib, jb) of the pixel is recorded. If there are a plurality of pixel addresses (ib, jb) at this time, the pixel address (ib, jb) extracted first is used in the same manner as described above. From the reflectance data of each pixel stored in the first memory 7a, reflectance data corresponding to the address (ib, jb) of this pixel is read out, and Rp (lowest density corresponding reflectance; reflectance as the reflectance) Save the value as the maximum). If there is a pixel with a print area ratio of 0%, the address (ib, jb) of that pixel is recorded, the subsequent detection operation is stopped on the spot, and the address (ib, jb) of that pixel is recorded. The reflectance data corresponding to the above may be read and stored as Rp. The above processing is performed by the reflection image data calculation unit 6 (see FIG. 7).

Next, the reflection image data calculation unit calculates the reflectance of each pixel using the Murray-Davis equation (2). In this process, since the pixels passing through the optical paths 23 and 24 shown in FIG. 18 depend on only the print area gradation, the reflectance of each pixel not including the optical dot gain can be calculated. Become.
R (i, j) = Ri * S (i, j) + Rp * (1-S (i, j)) (2)
R (i, j): Reflectance of pixel position i in the main scanning direction and pixel position j in the sub-scanning direction

  Finally, by converting the reflectance of all the images into the reflection density, the converted reflected image density has the same format as the reflected image data read by a normal image reading apparatus. By aligning the format, the reflected image density after conversion is stored in a recording medium such as a hard disk of a computer through the interface 10, or the reflected image density data is sent to the image output device 9. It is possible to reproduce an image.

  Hereinafter, specific examples will be described. In this embodiment, a CS-3910 having 1.34 million pixels, which is a CCD as a light receiver, is mounted, and 1 unit which is a moving unit to the main scanning of the optical system unit 30 is 1.3 mm. One unit which is a moving unit in the direction is set to 1.03 mm. FIG. 11 shows an example of reflected image data of a document on which an image is formed on a coated paper with a toner color material using an electrophotographic process. Hereinafter, description will be made taking this one dot (coloring material region in FIG. 11) as an example. The reflected image shown in FIG. 11A shows a situation where an optical dot gain is generated around the original dot shape under the influence of the optical paths 23 and 24 shown in FIG. The measurement result of the reflectance of each pixel at this time is FIG. 11B, and the value entered in each pixel is the reflectance. This processing was stored in the first memory 7a (FIG. 7) for the reflectance of all the pixels of the document that were repeatedly acquired while moving the optical system unit.

  FIG. 12 shows one dot which is a part of the transmission image of the document at the same position as FIG. As shown in FIG. 12A, unlike the reflection image, the blurring of the dot boundary due to the optical dot gain is hardly seen. The measurement result of the transmittance of each pixel at this time is shown in FIG. 12B, and the value written in each pixel is the transmittance. This processing was stored in the second memory 7b (FIG. 7) for the transmittance of all the pixels of the document that were repeatedly acquired while moving the optical system unit 30.

  FIG. 13 is a diagram illustrating a result of conversion from the measured transmittance of one dot to the print area ratio. The value written in each pixel is the print area ratio. As shown in FIG. 13 (a), Tmax was 70% and Tmin was 0% from the transmittance of each pixel stored in the second memory 7b. FIG. 13B shows the result of calculating the print area ratio of each pixel from the equation (1) using this value.

  FIG. 14 shows the reflectance of the pixel with the highest density (the reflectance corresponding to the highest density) covered with the color material, and the reflectance of the pixel with the lowest density in the pixel only with no color material (paper). The result which calculated | required Rp which is a reflectance corresponding to a minimum density) is shown. FIG. 14A shows the reflectance, and FIG. 14B shows the printing area ratio. Actually, the pixel having the highest value and the lowest pixel are searched from the print area ratio of each pixel stored in the third memory 7c, and the addresses (ia, ib) and (ib, jb) of the pixels are recorded. For convenience, in the case of an image of 1 dot, the printing area ratio S of the pixel at the address (2, 3) is 100% and the printing area ratio S of the pixel at the address (0, 0) is as shown in FIG. It became 0%. When the reflectances corresponding to these addresses are referred to in FIG. 5A, Ri (maximum density corresponding reflectance) corresponding to the highest density pixel (address (2, 3)) is 10, and lowest density pixel (address (0)). , 0)), Rp (reflectance corresponding to the lowest density) was 90.

  FIG. 15 shows the result of calculating the reflectance of each pixel by removing the optical dot gain from the equation (2). The result calculated from the previously obtained Ri and Rp and the print area ratio of each pixel is the center data. The value written in each pixel is the calculated reflectance. With the above processing, it was possible to read a clear image in which the dot edge portion did not blur due to the optical dot gain. The reflected image data was taken into a PC and output by a printer, so that an accurate image output sample could be produced. Although this image reading method is mainly described in the case of a monochrome image, it can also be realized in a color image by repeatedly processing the same content for each RBG. Further, even if this image reading method is incorporated in an image reading apparatus of an MFP (multifunction printer), the same result can be obtained.

FIG. 3 is a diagram illustrating an upper part and a lower part of the image reading apparatus. Sectional drawing of an image reader (at the time of reflection). The internal view of the upper part of an image reading apparatus. FIG. 3 is a cross-sectional view of the optical system of the image reading device (when reflected). FIG. 2 is a cross-sectional view of an optical system of the image reading apparatus (when transmitting). The figure which shows the flowchart of an image reading method. FIG. 3 is a control block diagram of the image reading apparatus. The graph which shows the relationship (coat paper) of the transmittance | permeability and a toner area ratio. The graph which shows the relationship (64g paper) of the transmittance | permeability and a toner area ratio. The graph which shows the relationship (128g paper) of the transmittance | permeability and a toner area ratio. The figure which shows the result of having acquired reflection data. The figure which shows the result of having acquired transmission data. The figure which shows the result of having calculated the printing area ratio. The figure which shows the result of having calculated Ri and Rp. The figure which shows the result of having calculated the reflection data of each pixel. The movement diagram of the light receiving CCD unit. Sectional drawing of an image reader (at the time of reflection). FIG. 4 is a diagram for explaining an optical dot gain occurrence phenomenon.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image reading apparatus 2 Reflected image reading part 3 Transmission image reading part 4 Light source output device 5 Print area ratio calculation part 6 Reflected image data calculation part 7 Memory 8 Image output apparatus 9 Interface 10 Control part 11 Host computer 21-24 Optical path 30 Optical System unit 31 Light source for reflection and light receiving CCD unit 32 Light source for transmission 33a, 33b Positioning member in main scanning direction 34a, 34b Positioning member in sub scanning direction 41 Operating belt (main scanning direction)
42 White film for reflection 42a White surface 42b Black surface 43 Rotating roller 44 Support wire 45 Support roller 46 Operation belt (sub scanning direction)
T (i, j) Transmittance of pixel at address (i, j) S (i, j) Printed area ratio of pixel at address (i, j) Ri Maximum reflectance corresponding to minimum density Rp Minimum density corresponding reflectance R (i , J) Reflectance of pixel at address (i, j)

Claims (8)

  An image area ratio calculation unit that obtains an image area ratio for each pixel as a ratio occupied by an image forming area based on transmission image data obtained by receiving transmitted light transmitted through the document, and a predetermined value for the document Is corrected for each pixel on the basis of the reflected image data obtained by receiving the reflected light from the original and the image area ratio obtained by the image area ratio calculator. An image reading apparatus comprising a reflected image data calculating unit for obtaining corrected reflected image data.   The image area ratio calculation unit obtains the image area ratio by using a predetermined function with the transmittance of each pixel constituting the transmission image data as a variable. Image reading device.   The function is a linear function of the transmittance that converts the image area ratio of the two pixels indicating the maximum transmittance and the minimum transmittance of the transmittance corresponding to 100% and 0%, respectively. The image reading apparatus according to claim 2.   The reflection image data calculation unit calculates the reflectance as the reflection image data included in each of the pixels indicating the minimum transmittance and the maximum transmittance in the transmission image data, and reflects the reflectance corresponding to the highest density. The density-corresponding reflectance is determined, and for each pixel, the image area ratio of the pixel and its complementary image area ratio are weighted and added to the highest density-corresponding reflectance and the lowest density-corresponding reflectance. The image reading apparatus according to claim 2, wherein the corrected reflected image data is calculated.   One light source, a first waveguide for guiding light from the light source to a transmission irradiation unit to obtain the transmission image data from the document, and from the light source to obtain the reflection image data from the document And the first waveguide for setting the output of the light source according to whether the transmission irradiation unit or the reflection irradiation unit is operated. The image reading apparatus according to claim 1, further comprising a control unit that selects one of the second waveguides.   The image reading device according to claim 1, wherein the control unit performs control so as to read image data within a predetermined range as the transmission image data or the reflection image data. apparatus.   The image reading apparatus according to claim 1, wherein the control unit integrally controls the transmission irradiation unit and the reflection irradiation unit.   The image reading apparatus according to claim 1, wherein the control unit controls to read the reflected image data first and then read the transmitted image data.

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